ABSTRACT
Low-molecular-weight organogelators (LMOGs) are interesting materials whose applications are diverse. These materials self-assemble through the formation of non-covalent intermolecular interactions to form supramolecular assemblies that trap solvent within their matrices. Because of the non-covalent nature of the forces of self-assembly, the gelation process is typically thermally reversible. In this chapter, various types of organogelators, mainly including examples of organogelators grafted with amide functionalities utilized for the formation of hybrid structures with various applications discussed. The construction of the gel structure in the amide-functionalized organogelators is mainly based on the intermolecular hydrogen bonding between amide groups with bestowed support of aromatic p−p stacking, and van der Waals interactions.
Supramolecular chemistry is a highly interdisciplinary field that has rapidly developed in the last two decades. In general, supramolecular chemistry concerns non-covalent interactions. The word “non-covalent” compasses an enormous range of attractive and repulsive effects and it can be defined as “spontaneous association of two or more molecules or ions to create an aggregate species by reversible interactions.” Supramolecular gels are semi-solid materials, which can serve a variety of purposes and are permeated ubiquitously in our daily lives in a variety of forms. Gels are prevalent in nature, within cells and tissues of bodies, and are also present in variety of artificial materials including toothpaste, soap, shampoo, hair gel, contact lenses and gel pens, etc. Although gels are abundant and widely studied, the exact definition of a gel was often a contention among scientists. The word “gel” is derived from the Latin word “gelâre” meaning “to freeze.” A more compact definition given by P. J. Flory defined a gel as “a colloidal dispersion with a continuous structure over macroscopic dimensions, which is permanent on the analytical time scale, and which is solidlike in its rheological behavior”.1 The colloidal dispersion causes an increase of the viscosity in the liquid medium by forming a matrix that entraps the liquid. Because of that, the system attains a semi-solid consistency and lies between the liquid and solid state. Most of the early findings on molecular gels were serendipitous, e.g., from failed crystallization attempts. However, over the years, insights gained on the self-assembly of molecules facilitated the design of a variety of molecules that form strong gels with intriguing properties. 5.2 Classification of Gels
